Positioning an ophthalmic device a known distance from an eye being examined is typically of great importance. In many devices one reason for this precise positioning is to have features of the eye in clear focus—potentially for subsequent interaction with the image by an operator or software. Other reasons include the need to have a laser beam come to focus at the correct plane with respect to the eye (for example in an excimer laser system) or to have the eye optimally positioned for subsequent measurement of the eye (for example a wavefront measurement).
A number of techniques are used to assist in eye-to-device positioning. These include the breaking of light beams (usually IR) by the corneal apex and the projection onto the cornea of a number of light beams, which can subsequently be analyzed either automatically or by an operator to assess accuracy of eye positioning. If the eye is deemed to not be in the optimal position then the device and/or head/eye can be moved so as to reposition the eye optimally or to within defined acceptable tolerances.
The application of lasers and other like ophthalmic devices to diagnose conditions of the eye has opened new possibilities for treating nearsightedness, farsightedness, astigmatism, and other conditions of the eye. Specifically, Laser technology has allowed the development of modern laser techniques that are collectively known as laser vision correction.
Laser vision correction techniques reshape the surface or subsurface of eye 10 as shown in FIG. 1. These techniques may employ a cool beam of light (such as Excimer laser beam 12) to remove microscopic amounts of tissue. The removal of this tissue changes the shape of cornea 14 in order to allow sharper focusing of images and reducing a patient's dependence on glasses and/or contact lenses. Laser vision correction surgeries include, but are not limited to, laser-assisted in situ keratomileusis (LASIK), laser epithelial keratomileusis (LASEK), epi-LASIK, automated lamellar keratoplasty (ALK), photo ablation procedures such as photo refractive keratectomy (PRK), and other like procedures.
In these procedures, the quality of the results of the laser vision correction may depend upon the ability of the laser 12 to precisely remove tissue from the surface or beneath the surface of cornea 14. Accurately removing tissue with laser 12, in turn may at least in part depend on the ability to accurately align and position the laser and other imaging systems with reference to the eye undergoing the procedure.
One of the most time consuming portions of the procedure is the set up and positioning of the laser. Existing procedures may utilize manual techniques to align the laser prior to the laser vision correction. Additionally, laser vision correction procedures often require alignment of the laser between individual patient's procedures or between an individual patient's eyes. Also, there may be a need to determine the positioning of the device during the procedure.